1. Field of the Invention
The present invention relates to a fuel injection apparatus, which includes a piezoelectric actuator as a drive source and injects high pressure fuel.
2. Description of Related Art
Lately, it has been demanded to adjust a fuel injection quantity (amount) at a high accuracy and to achieve a quick operational response in a fuel injection apparatus, which injects high pressure fuel in a cylinder of an internal combustion engine of a vehicle (e.g., an automobile) to reduce emissions in exhaust gas or to improve fuel consumption. In order to meet the demand of the improved fuel injection accuracy and the improved operational response in the fuel injection apparatus, there have proposed various fuel injection apparatuses, which have a piezoelectric actuator of a larger force and of a further improved operational response.
WO2005/075811A1 (corresponding to US 2007/0152084A1) teaches a fuel injection valve (injector), which injects fuel into a cylinder of an internal combustion engine. The fuel injection valve includes an injector base body, a nozzle holder and a valve element. The valve element is slidably received in the nozzle holder and has a seat surface, which is adapted to open or close a fuel injection hole. A piezoelectric actuator drives the injection valve element. More specifically, the piezoelectric actuator drives a first piston, which receives a second piston that is connected to the injection valve element.
JPH11-200981A teaches a fuel injection valve and a drive method thereof In the fuel injection valve, a first pressure receiving surface, which is directed downward and is formed by a step between a first guide shaft and a second guide shaft of a needle 15, is communicated with or is disposed in a control pressure chamber, a pressure of which is changed depending of displacement of an electrostrictive actuator. The voltage, which is applied to the electrostrictive actuator, is changed several times within one injection time period to change a fuel injection rate, which is determined by the lift amount of the needle, several times within the one injection time period.
In the prior art fuel injection apparatus, which uses the piezoelectric actuator, the pressure, which is applied to the piezoelectric actuator, changes in response to the drive movement of the needle, so that a voltage is generated in a direction opposite to that of the drive voltage due to the piezoelectric effect. In this way, the drive speed of the fuel injection apparatus may possibly be slowed down to cause a reduction in the response speed and a reduction in the fuel injection accuracy.